Pseudogene of dihydrolipoyl succinyltransferase (E2k) found by PCR amplification and direct sequencing of rodent-human cell hybrid DNAs

Previous studies have indicated that the cDNA for the E2k component of the human alpha-ketoglutarate dehydrogenase complex (KGDHC) hybridized not only to a major locus on chromosome 14q24.3 in a region associated with familial Alzheimer's disease and with Joseph-Machado disease, but also to another locus on chromosome 1p31. We now report that PCR of genomic DNA and direct sequencing indicated that the chromosome 1 locus is an intronless pseudogene. PCR of genomic DNA amplified E2k fragments from mouse-human cell hybrids containing human chromosome 1 DNA but not from hybrids containing human chromosome 14 DNA. The resulting amplicons were of comparable sizes to those when the cDNA was used as template. The direct sequencing of these amplicons confirmed the lack of introns and indicated a frame shift, which led to the presence of four termination codons early in the coding region. PCR followed by direct sequencing of the amplicons appears to be a convenient method for identifying intronless pseudogenes.